Note that ImageJ is constantly evolving so there is no single book on ImageJ that covers all functions, macros and plugins available. That being said, the ImageJ User Guide is available on the ImageJ website. The following are some of other resources available:

The Online Manual for the MBF-ImageJ collection by Tony Collins describes the collection of plugins available from the McMaster Biophotonics Facility website. (Many of those plugins are also available from other sites).